Journal of Bone and Mineral Research最新文献

Cerebral palsy (CP) is a non-progressive neurological syndrome resulting in abnormal muscle tone, movement, and posture. It is unclear whether ambulatory children with CP have deficits in bone quantity or quality. Furthermore, the relationship between abnormal muscle tone, altered function, and bone health remains largely unexplored. This observational study investigated bone mineral density (BMD) and microarchitecture in ambulatory children with spastic CP and associations of BMD with function, muscle spasticity, and gait. Children with spasticity in both lower limbs (n = 12) aged 3-8 years were recruited. Areal BMD was measured with dual-energy x-ray absorptiometry (DXA) at the proximal femur and lateral distal femur and compared to normative data. High-resolution peripheral quantitative computed tomography (HR-pQCT) was performed at the metaphyseal tibia and radius in a subset of participants (n = 5) and compared to healthy children (n = 7). Gait pathology and cardiopulmonary function were investigated with the Gait Deviation Index, Edinburgh Visual Gait Score, and energy expenditure index. DXA aBMD Z-scores at the lateral distal femur were within a normal range. Instead, the CP group's median aBMD Z-score at the proximal femur was -1.8 (interquartile range: -2.2, -1.2, p=.03) indicating potential skeletal fragility. Strong correlations were found between gait pathology and DXA-based bone outcomes (correlation coefficient 0.62 (p=.04) to 0.73 (p=.01)) as well as energy expenditure index and DXA-based bone outcomes (correlation coefficient -0.63 (p=.03) to -0.98 (p = <0.001)). At the metaphyseal tibia, children with spastic CP had significant deficits in HR-pQCT-measured bone geometry and trabecular microarchitecture: 35% lower total area, 42% lower trabecular area, and 48% lower trabecular number than controls. HR-pQCT parameters were similar between groups at the metaphyseal radius. These differences in tibial metaphysis size and trabecular microarchitecture are similar to those observed in disuse and thus could be a result of abnormal biomechanics or low levels of physical activity.

Osteogenesis imperfecta (OI) Type V is typically characterized by radial head dislocation, calcification of interosseous membrane and hyperplastic callus. It is caused by the c.-14C > T mutation in the 5' UTR of IFITM5 gene, adding five amino acids (MALEP) to the N-terminal of IFITM5 protein. Previous studies have suggested a neomorphic function of the MALEP-IFITM5 protein. However, the underlying mechanisms remain unclear due to embryonic lethality in previous mouse models. Therefore, we developed an inducible mouse model (Ifitm5flox c.-14C > T) that could be induced by Cre expressed at different developmental stages to explore the pathogenic effects of the neomorphic MALEP-IFITM5. The mutant Ifitm5 allele could be regulated by the endogenous regulatory elements after Cre recombination, maintaining its spatiotemporal expression pattern and physiological level. Specifically, Prx1-Cre; Ifitm5flox c.-14C > T mutant mice were born with fractures in all limbs, showing impaired ossification and enhanced chondrogenesis associated with increased SOX9 abundance. Analyses of single-cell RNA sequencing data revealed arrested osteogenesis in Prx1-Cre; Ifitm5flox c.-14C > T mouse. A major population of cells expressing both osteogenic and chondrogenic signature genes was identified in the mutant mouse. Reduced expression of SP7 and SOST in the cortical regions of mutant mice confirmed delayed osteocyte maturation and compromised osteogenesis. Elevated bone marrow adipocytes were found in the adult mutant mice. Ectopic chondrogenesis and SOX9 expression were also observed in the perichondrium regions of Col1a1-Cre; Ifitm5flox c.-14C > T and Ocn-Cre; Ifitm5flox c.-14C > T mutant mice. The inducible Ifitm5flox c.-14C > T mouse model and integrated single-cell transcriptomic analyses elucidated that ectopic expression of SOX9 and disrupted homeostatic balance among osteogenesis, chondrogenesis and adipogenesis may contribute to the pathogenesis caused by MALEP-IFITM5, helping to gain deeper insights into the molecular mechanisms of type V OI.

Cementocytes are terminally differentiated cells embedded in cellular cementum, an important hard tissue covering the apical regions of tooth roots. However, the roles of cementocytes in cellular cementum remain enigmatic. Here, we show that Murine Double Minute 2 (Mdm2), an E3 ubiquitin ligase that plays vital roles in regulating cell proliferation, apoptosis, and differentiation to influence tissue or organ development, is highly expressed in the cementocytes of mice. To investigate the role of cementocyte-expressed Mdm2, Dmp1-Cre;Mdm2flox/flox (Mdm2 cKO)mice were obtained to inactivate Mdm2 in cementocytes. The results showed that Mdm2 was successfully ablated and Mdm2 cKO mice display increased cementocyte apoptosis and reduced cellular cementum volume. p53, the canonical substrate of Mdm2, was accumulated and hyperactivated in the cementocytes of Mdm2 cKO mice and in cultured IDG-CM6 cells (a cementocyte cell line) treated with Nutlin3a, an inhibitor of Mdm2. Further experiments showed that inactivation of one allele of p53 significantly rescued the increased cementocyte apoptosis and the decreased cellular cementum volume in Mdm2 cKO mice. Therefore, p53 is targeted by Mdm2 for degradation and mediates the role of Mdm2 in cementocyte survival and cellular cementum volume. Notably, Mdm2 cKO mice exhibited decreased differentiation of cementoblasts (the cell type primarily responsible for cementum deposition) and reduced rate of cellular cementum deposition. Meanwhile, OCCM-30 cells (a cementoblast cell line) showed diminished migration, proliferation, differentiation, and mineralization ability after culture with conditioned medium (CM) from Nutlin3a-pretreated IDG-CM6 cells. Intriguingly, Mdm2 cKO mice displayed significantly increased osteoclast formation and cementum resorption. Meanwhile, in vitro experiments verified that CM from Nutlin3a-pretreated IDG-CM6 cells induced osteoclast differentiation of bone marrow macrophages. Collectively, these results demonstrate that Mdm2-mediated degradation of p53 promotes cementocyte survival, and that cementocytes affect the cell behaviors of cementoblasts and osteoclasts through a paracrine mode to modulate cellular cementum volume.

Bone homeostasis within the skeletal system is predominantly maintained by bone formation and resorption, where formation of new bone involves maturation of stromal cells to mineral and matrix secreting mature osteoblasts, which requires cellular energy or adenosine triphosphate. Alterations in systemic metabolism can influence osteoblast function. In line with this, type 2 diabetes mellitus (T2DM), a common metabolic disorder is also associated with reduced bone formation and increased risk of fracture. Impairment in lipid metabolism is one of the key features associated with T2DM-related pathologies in multiple tissues. Therefore, we tested the hypothesis that the reduced bone formation reported in obese murine models of impaired glucose tolerance is a function of disrupted lipid metabolism in osteoblasts. We first confirmed that mice fed a high-fat diet (HFD) have reduced bone microarchitecture along with lower bone formation rates. Interestingly, osteoblasts from obese mice harbor higher numbers of cytosolic lipid droplets along with decreased bioenergetic profiles compared to control cells. Further supporting this observation, bone cortex demonstrated higher total lipid content in HFD fed mice compared to control-fed mice. As a further proof of principle, we generated a novel murine model to conditionally delete Plin2 in osteoblast-progenitor cells using Prrx1-Cre, to enhance lipid droplet breakdown. Our data demonstrate that knocking down Plin2 in an osteoprogenitor specific manner protects from HFD induced osteoblast dysfunction. Furthermore, the mechanism of action involves enhanced osteoblast fatty acid oxidation. In conclusion, the current studies establish that HFD induced glucose intolerance leads to perturbations in osteoblast lipid metabolism, thus causing lower bone formation, which can be protected against by increasing fatty acid oxidation.

Motivated by studies showing an association between beta blocker (BB) use and positive bone outcomes, a pilot randomized control trial was performed at the Mayo Clinic which randomized postmenopausal women to placebo, propranolol (40 or 80 mg twice daily), atenolol (50 mg/d), or nebivolol (5 mg/d) to determine changes in bone turnover markers (BTMs) and in BMD over 20 wk. Pharmacogenetic effects and microRNA-mediated mechanisms involving beta adrenergic receptor and related genes have previously been found. We sought to validate these effects and discover new candidates in an ancillary study to the pilot clinical trial. We genotyped all participants and performed microRNA (miRNA) sequencing at baseline and at 20 wk for 24 participants from the atenolol or placebo groups. We discovered several variants in ADRB1, ADRB2, and HDAC4 which showed significant pharmacogenetic effects with BMD at multiple sites and with BTMs. Our miRNA results showed a significant treatment effect for miR-19a-3p over time with atenolol use in the low-responder group compared to placebo. Overall, the longitudinal miRNA analysis showed a large number of miRNAs which were up-regulated over the trial in the low responders but not the high responders compared to placebo, of which miR-19a-3p was one example. Finally, we compared the response to atenolol treatment for cardiovascular traits (pulse and blood pressure) with the response for the bone resorption marker, C-terminal telopeptide, and found a largely independent effect. Our results have implications for personalized therapy and for understanding mechanisms of BB treatment effect on bone.

Autosomal dominant hypocalcemia (ADH) is due to enhanced calcium-dependent signaling caused by heterozygous gain-of-function (GOF) variants in the CASR gene (ADH1) or in the GNA11 gene, encoding Gα11 (ADH2). Both ADH1 and ADH2 are associated with hypocalcemia and normal or inappropriately low levels of circulating PTH. ADH1 patients typically manifest hypercalciuria, while ADH2 is associated with short stature in approximately 42% of cases. We evaluated a 10-yr-old boy with hypoparathyroidism and short stature. Biochemical analyses revealed hypocalcemia, hyperphosphatemia, and inconsistent hypercalciuria. Genetic analyses revealed a de novo heterozygous p.Leu723Arg variant in CASR. We characterized the expression of recombinant WT and Leu723Arg calcium-sensing receptor (CaSR) proteins in HEK293 cells and assessed G protein activation in vitro by CaSR using bioluminescence resonance energy transfer. Transient expression studies showed the Leu723Arg variant was normally expressed but resulted in a significantly lower EC50 for extracellular calcium activation of G11 but not other G proteins (ie, Gi, Gq, Gs). The Leu723Arg substitution has a novel GOF phenotype that leads to biased CaSR activation of G11 signaling, suggesting that residue 723 specifies activation of G11 but not other G proteins. Similar studies of a previously described CaSR variant associated with hypoparathyroidism and short stature, Leu616Val, showed no changes in any G protein pathways, indicating it is likely to be a benign variant. Given the preferential activation of G11 by the Leu723Arg CaSR variant, we propose that the patient's short stature shares a similar basis to that in patients with ADH2 due to GOF variants in GNA11.

Atypical femur fractures (AFFs) have been reported with long-term use of anti-resorptive drugs. Early identification is crucial because it allows early intervention to stop the progression to complete fracture, thus potentially reducing the ensuing burden. It has been shown that extending the scan image to take a full-length image of the femur (FFI) using single energy (SE) X-rays at the time of a dual-energy X-ray absorptiometry (DXA) scan can detect findings in the spectrum of AFF. Following the International Society for Clinical Densitometry (ISCD) recommendations, FFI by SE X-ray is being performed for all patients who present to the Calcium Metabolism and Osteoporosis program at AUBMC for bone mineral density measurement by DXA, if they have received anti-resorptive drug for a cumulative period of 3 years or more. Patients can be currently on anti-resorptive drug or have discontinued it within the past 5 years prior to scan, instead of the 1 year, as recommended by the ISCD. The primary aim of this retrospective study was to assess the prevalence of findings in the spectrum of AFF using FFI by SE X-rays. We collected data on demographic factors, clinical risk factors for osteoporosis, and bone densitometry parameters. Out of the 948 patients, 18 patients were found to have findings in the spectrum of AFF; 14 underwent subsequent imaging studies to investigate and confirm these abnormalities. One patient out of 948 patients was found to have an incomplete AFF confirmed by computed tomography scan. Studying the prevalence of the signs of AFF on FFI in other studies and assessing the specificity of this technique by comparing its findings with more established methods is important. Future ISCD task forces may need to reassess efficacy and cost effectiveness of its recommended guidance on using SE femur in patients to prevent adverse outcomes.

X-linked osteoporosis, caused by PLS3 genetic variants, is a rare bone disease, clinically affecting mainly men. Limited data are available on bone microarchitecture and genotype-phenotype correlations in this disease. Our aims were to assess bone microarchitecture and strength in adults with PLS3 variants using high-resolution peripheral quantitative computed tomography (HR-pQCT) and to explore differences in the phenotype from HR-pQCT between PLS3 variants. HR-pQCT scans were obtained from the distal radius and tibia of 13 men and 3 women with PLS3 variants. Results were compared with age- and sex-matched controls from a normative dataset from literature and expressed as Z-scores. Median age was 46 yr for men and 48 yr for women. In men, total bone area was large (median Z-score: 1.33 radius; 1.46 tibia) due to a large trabecular area (+1.73 radius; +1.87 tibia), while the cortical area was small (-2.61 radius; -2.84 tibia). Total volumetric bone mineral density (BMD) was low due to low trabecular (-3.46 radius; -3.37 tibia) and cortical BMD (-2.87 radius; -2.26 tibia). Regarding bone microarchitecture, the largest deviations were found in trabecular number (-2.18 radius; -1.64 tibia), trabecular separation (+2.32 radius; +1.65 tibia), and cortical thickness (-2.99 radius; -2.46 tibia), whereas trabecular thickness and cortical porosity were normal (-0.36 and -0.58 radius; 0.09 and -0.79 tibia). Additionally, failure load was low (-2.39 radius; -2.2 tibia). Results in the women deviated less from normative data. Men with frameshift/nonsense variants seemed to have more deviant trabecular and cortical microarchitecture and strength, at both scan locations, than those with missense/in-frame insertion variants. In conclusion, HR-pQCT provides valuable insights into bone area, BMD, microarchitecture, and strength in adults with PLS3 variants and can be used to explore genotype-phenotype relationships. Longitudinal analyses in larger groups are needed to study the natural course of the disease and treatment effects.

A 58-yr-old woman presented to our mineral metabolism center, complaining of localized and continuous pain, which worsened with movements, and weakness of the right foot. The patient reported having had a fracture of the fifth metatarsal bone of the right foot about 4 mo ago. She was initially treated with a cast that she did not tolerate and then with an orthopedic brace. After about 1 mo, she noticed swelling of the right foot and started complaining of continuous pain. The physical examination when came to our center seemed partly improved in respect to the initial one referred by the patient even though she still presented with a mild swelling, reddish skin color, and mild sweating on the right foot. Allodynia and hyperalgesia still persisted but at a lower grade. Main biochemical parameters of calcium metabolism were in the normal range. After excluding other clinical conditions, a diagnosis of complex regional pain syndrome type I was made. She was treated with neridronate iv with resolution of symptoms while continuing with physical therapy and pain relievers. Similar milder episodes were reported by the patient in the following months. However, they were immediately resolved by prompt neridronate infusion. No further complaints have been reported during the next 3 yr follow-up.